In many solid ink printheads, the nozzle plate and jet stacks typically consist of stainless steel plates. The nozzle plate has an array of small holes, or nozzles, also sometimes referred to as jets, through which the ink exits the jet stack. Stainless steel nozzle plates and other plates in the jet stack are being replaced with flexible, polymer layers such as polyimide. In some instances, the polyimide film receives an anti-wetting coating, is bonded to a stainless steel aperture plate, and then a laser ablates the array of apertures into the polyimide film.
Drooling nozzles, wetting and adhesion of ink on the printhead front face lead to missing and misdirectional jetting along with poor IQ. Drooling nozzles weep ink when the internal pressure of the printhead exceeds a particular pressure, typically measured in inches or water. The higher pressure the nozzles can maintain without weeping leads to higher jetting latitude and improved performance. Wetting occurs when the front face of the printhead remains wet after printing. This ink that remains on the printhead can block the nozzles resulting in missing nozzles and misdirectional printing. FIG. 1 shows a photograph of such a contaminated printhead.
Currently, one approach to overcome these issues is to use an active cleaning blade system. The system purges ink from the printhead and a wiper blade then wipes the ink off the front face. Ink purges typically occur after the system detects missing jets and after a power-down when the ink has frozen or solidified, shrunk and drawn air into the system. The ink purge expels contamination, trapped air and clears the nozzles, and then the wipers clean off the front face. To meet future EnergyStar® requirements, the printers will shutdown nightly during which the printheads, reservoirs, and umbilicals do not receive heat. With an expected printhead lifetime of 6 years, daily purges will require roughly 2000 purge and wipe cycles. This increase in wipes means that any anti-wetting coating will have to survive and maintain their beneficial properties for over 2000 cycles.
The anti-wetting coating must have high contact angle to maintain adequate drool pressure and low slide angle to maintain the easy clean/self clean feature. This will lead to printhead cartridges with low or no maintenance, high engine reliability and low run cost. The stack manufacturing process generally involves high temperatures and pressures, so the coating must maintain these properties under these conditions, typically 290° C. and 350 psi for approximately 30 minutes. Generally low-adhesion coatings having low slide angles have shown to slide off the printhead front face cleanly under gravity.
Oleophobic, low adhesion surface coatings have provided significant performance improvements. However, even with such a coating, printhead front face will undergo several wipe cycles. Current coatings, while having good thermal and ink stabilities, may suffer from lower mechanical robustness than may be desirable.
Another issue may arise with these coatings. After high temperature curing processes used in some of the above approaches, the coating may have a thin layer of oil on its surface. While the oil does not seem to detrimentally affect the surface properties and printhead performance, it may cause shelf life issues and present problems in packaging and handling. One could clean off the oil layer, but that increases manufacturing complexity and costs.